When the temperature and relative humidity of air entering
and leaving the Prometeo HR400 unit are such that frost may form
on the heat exchanger surface, the efficiency
of the unit can be affected.

The Prometeo HR400 automatically controls the fan speed to allow
defrosting in low temperatures, in particularly harsh climates this may not solve the problem. In such cases where the outdoor air temperature drops below minus 9 degrees centigrade, Vortice
recommend the installation of a 500W pre-heater on the air
intake duct to warm the incoming air.

The Prometeo 500W heater will operate automatically for the minimum time needed to solve any frosting problems.